BIGHEARTED DE NIRO LAYS IT ON THE LINE TO SIZEMORE

Sizemore, the star of "Black Hawk Down," has been down in the dumps over recent run-ins with the law, so the veteran Oscar winner talked to him, hoping to straighten him out.

HOT WATER

The 39-year-old actor landed in hot water recently when he reportedly tested "dirty" for methamphetamine use.

The Los Angeles City Attorney's office filed a notice of probation violation against the troubled actor -- who still has to serve a minimum of 90 days for domestic abuse against his former girlfriend, infamous Hollywood madam Heidi Fleiss.

But "Analyze That" star De Niro analyzed his pal's problems and decided to give him some advice, revealed an insider. The two met on the set of "Heat" in 1995 and have remained close.

"Robert took Tom for a drive and gave him a stern talking to," divulged the insider.

"Bobby asked him to seriously consider what the heck he was doing and what ramifications his negative actions would have on his life.

"De Niro said, 'Tom, what are the odds of becoming a movie star? Especially a guy like you.'

"Tom knows he's not 'box office beautiful' like Brad Pitt. He's got a gravelly voice and odd features. He used to wake up at 5 a.m. to take a New York subway to work -- where he'd cut melons for corporate breakfasts!

PUSHING HIS LUCK

"De Niro told him he was beyond lucky to have gotten as far as he had -- and he shouldn't throw it all away. Basically, he told Tom he was blowing it."

Sizemore confirmed to a reporter: "Bobby De Niro talked to me when I was having problems. He said you're going to ruin your life, your health . . . if you don't stop doing this stuff."

NEW SERIES

In April, a judge postponed Tom's jail sentence, ruling he could travel to Nevada to shoot the new CBS series "Dr. Vegas."